Unharvested Plots Research Articles

Retention forestry as a climate solution: Assessing biomass, soil carbon and albedo impacts in a northern temperate coniferous forest

Forest management pathways for nature-based climate solutions, such as variable retention harvesting (VRH), have been gaining traction in recent years; however, their net biochemical and biophysical impacts remain unknown. Here, we use a combination of close-range and satellite remote sensing, eddy covariance technique, and ground-based biometric measurements to investigate forest thinning density and aggregation that maintain ecosystem nutrients, enhance tree growth and provide a negative feedback to the local climate in a northern temperate coniferous forest stand in Ontario, Canada. Our results showed that soil carbon (C) and nitrogen (N) in VRH plots were significantly lower (p < 0.05) for all VRH treatments compared to unharvested plots. On average, soil C was reduced by −0.64 ± 0.22 Δ% C and N by −0.023 ± 0.008 Δ% N in VRH plots. We also observed the largest loss of soil C and N in open areas of aggregate plots. Furthermore, the changes in albedo resulting from VRH treatment were equivalent to removing a large amount of C from the atmosphere, ranging from 1.3 ± 0.2 kg C yr−1 m−2 in aggregate 33 % crown retention plots to 3.4 ± 0.5 kg C yr−1 m−2 in dispersed 33 % crown retention plots. Our findings indicate that spatially dispersed VRH resulted in minimal loss of soil C and N and the highest understory growth and C uptake, while enhanced tree growth and local cooling through increased albedo were observed in dispersed VRH plots with the fewest residual trees. These findings suggest that using the harvested trees from VRH in a way that avoids releasing C into the atmosphere makes dispersed VRH the preferred forest management pathway for nature-based climate solutions.

Increase in forest structural complexity along a precipitation gradient is mediated by partial harvests in temperate Patagonian forests

Increasing forest structural complexity is becoming a common goal in forestry worldwide. However, the lack of empirical quantification clouds its implementation. Here we quantified the long-term effects (> 30 y) of partial harvest on stand structural complexity and net primary productivity using the east–west precipitation gradient (318–2508 mm, mean annual precipitation-MAP) of western Patagonian as a study system. In this gradient, pairs of 1-ha plots on 20 sites (20 plots harvested and 20 plots unharvested) were installed. In each plot terrestrial laser scanning was used to quantify the stand structural complexity index (SSCI), and Sentinel satellite images to obtain the Enhanced Vegetation Index (EVI: proxy of net primary productivity). Generalized linear mixed-effect models were used to relate SSCI to MAP and EVI to SSCI, with harvesting as indicator variable, and site as random variable (two plots nested to same precipitation). Results showed that harvested plots on mesic-to-humid sites (but not on dry sites) had higher SSCI and EVI values compared to unharvested plots, likely due to a greater vertical canopy packing. These results show the influence of precipitation on SSCI, which resulted in a more diversified stand structure and higher EVI. Such insights support site-specific management aimed to increase forest structural complexity.

The size of clearings for charcoal production in miombo woodlands affects soil hydrological properties and soil organic carbon

Charcoal production is a major driver of forest degradation in miombo woodlands. Forests play a crucial role in regulating the hydrological cycle, so it is critical to understand how forest degradation and management practices impact water availability, particularly in drylands. Few studies have examined the effect of forest clearing size on the hydrological functioning of soil, particularly under real-world conditions where, following clearing, forests are subject to multiple and prolonged anthropogenic disturbances, as occurs in miombo woodlands which are cleared for charcoal production and commonly used for livestock grazing. The pilot project Transforming Tanzania's Charcoal Sector was established in 2012 with the aim of establishing a sustainable wood harvesting system for charcoal production based on rotational harvesting cycles that allow for natural forest regeneration. Two clearing sizes were established: large clearings (300 × 300 m) harvested by clear-felling, and small clearings (50 × 50 m) harvested in a checkerboard pattern. We examined the effect of these two clearing sizes on soil hydrological properties and soil organic carbon (SOC) in Kilosa district, Morogoro, Tanzania. Our analysis included four treatments: large clearings, small clearings, small intact plots (unharvested plots within the checkboard pattern), and village land forest reserve. For each treatment we assessed the tree cover and measured soil infiltration capacity, soil bulk density, SOC stock, and texture. We also examined the relationship between these variables and the distance to the closest road to better understand the impact of livestock and human disturbance. Our results show that large clearings had the lowest mean infiltration capacity (121 ± 3 mm h−1) and SOC stock content (12 ± 0.2 tonnes ha−1), and the highest bulk density (1.6 ± 0.005 g cm−3) of all the treatments. We found a positive relationship between infiltration capacity and basal area (R2 = 0.71) across all treatments. We also found that infiltration capacity, SOC stock and tree basal area increased with increasing distance from the closest road, while bulk density decreased. We conclude that, in terms of their impact on soil hydrological functioning and SOC stock, small clearings, while not completely unaffected, are better than larger ones. In small clearings, concurrent reductions in tree cover and a relatively low impact on soil hydrological properties could result in increased soil and groundwater recharge compared to unharvested forest areas. Controlling livestock grazing can further minimize soil degradation, producing additional gains.

Strip Clearcutting Drives Vegetation Diversity and Composition in the Moso Bamboo Forests

Abstract Strip clearcutting of Moso bamboo forests in southern China has seen increasing interest as a way of reducing harvesting costs. Previous research has shown that cutting influences the overstory structure and drives changes in the microclimate and soil properties. However, the effects of strip cutting on understory vegetation diversity and composition remain unclear. To better understand the influence of cutting on the understory vegetation, this study compares sites under natural restoration after cut and uncut sites in the Moso bamboo forest. We selected plots that were cut in 2019 (C19) and 2017 (C17), as well as unharvested plots as controls (CK). The results showed that strip clearcutting increased the understory vegetation richness and diversity, and a significant difference (A = 0.23, P = 0.001) existed in the composition of the vegetation between the three treatments. Furthermore, the decrease of soil total phosphorus and total potassium content resulted in the difference in undergrowth vegetation distribution and composition between the uncut plots and the cut plots. Our results suggest that strip clearcutting may not be harmful to biodiversity on a local scale in the Moso bamboo forest.

Functional Trait Responses to Strip Clearcutting in a Moso Bamboo Forest

Functional characteristics reflect plant strategies and adaptability to the changing environment. Determining the dynamics of these characteristics after harvesting would improve the understanding of forest response strategies. Strip clearcutting (SC) of moso bamboo forests, which significantly reduces the cutting cost, has been proposed to replace manual selective harvesting. A comparison of restoration features shows that 8 m is the optimal cutting width. However, the precise response of functional features to the resulting harvest-created gap remains unclear. In this study, three SC plots were selected which was performed in February 2019, with three unharvested plots as a control (C). The study focused on 10 functional traits, including leaf area (LA), specific leaf area (SLA), leaf dry matter content (LDMC), leaf nitrogen content (LNC), leaf phosphorus content (LPC), nitrogen/phosphorus ratio (N:P), wood density (WD), fine root biomass (FRB), specific fine root length (SRL), and root length density (RLD). A one-way ANOVA was used to compare differences in functional traits and soil nutrients between treatments. Strip clearcutting significantly reduced the soil organic carbon (SOC) and total nitrogen (TN) contents (p &lt; 0.05). In terms of functional characteristics, SC significantly decreased LA and increased LNC, LPC, and N:P (p &lt; 0.05). However, SC had no significant effect on fine root traits (p &gt; 0.05). This study highlighted that root trait, soil content of total phosphorus (TP) and total potassium (TK) returned to the level of uncut plots after a year’s recovery. The LPC, LNC, and N:P were negatively correlated with LA, and LDMC and WD were negatively correlated with SLA, while the effect of SC on fine root traits was limited (p &gt; 0.05). Fine root traits (FRB, RLD, and SRL) were positively associated with SOC, TN, and TP, but negatively correlated with TK. The changes in soil nutrient content caused by the removal of biomass were normal. Increased light and the rapid growth of new trees will increase nutrient regressions; therefore, these results further confirm the feasibility of SC.

Structure, composition and regeneration of miombo woodlands within harvested and unharvested areas

Production of tobacco by small holder farmers in Zimbabwe after the year 2000 land reform programme impacted woodlands due to the widespread use of fuel wood instead of coal for tobacco curing, but impacts have been rarely quantified. We assessed the effect of fuel wood harvesting for tobacco curing on structure, composition and diversity in harvested and unharvested miombo woodlands in the central watershed of Zimbabwe. Tree size class distributions provide demographic information on regeneration and recovery from disturbances. Vegetation structure and plant species composition were assessed in thirty 20 × 20 m plots in each site. Tree basal area, canopy cover and height were significantly higher in the less disturbed unharvested compared with harvested site. Species composition differed between harvested and unharvested sites, with higher diversity in the harvested compared with unharvested site. Trees had reverse-J-shaped size class distribution curves for both stem diameter and height at the harvested site and bimodal distributions with fairly large densities in larger size classes at the unharvested site. Recruitment and regeneration were higher in the harvested than unharvested site. Our findings show that harvesting fuel wood for tobacco curing has negative effects on tree structure, but not yet the diversity of the miombo woodland, however the latter will likely negatively impact tree species favoured for harvesting over the medium-long term. When species composition was compared using NMDS ordination, the harvested and unharvested plots were distinctly separated. Because of the rotational time for miombo woodlands of >25 years, continuous harvesting of the woodland may permanently keep the trees small, failing to provide sufficient wood for tobacco curing. Therefore, there is need for the consideration of alternative or supplementary sources of energy such as solar, with a zero deforestation in the production chain of tobacco in the whole miombo eco-region.

Aboveground forest carbon shows different responses to fire frequency in harvested and unharvested forests.

Sequestration of carbon in forest ecosystems has been identified as an effective strategy to help mitigate the effects of global climate change. Prescribed burning and timber harvesting are two common, co-occurring, forest management practices that may alter forest carbon pools. Prescribed burning for forest management, such as wildfire risk reduction, may shorten inter-fire intervals and potentially reduce carbon stocks. Timber harvesting may further increase the susceptibility of forest carbon to losses in response to frequent burning regimes by redistributing carbon stocks from the live pools into the dead pools, causing mechanical damage to retained trees and shifting the demography of tree communities. We used a 27-yr experiment in a temperate eucalypt forest to examine the effect of prescribed burning frequency and timber harvesting on aboveground carbon (AGC). Total AGC was reduced by ~23% on harvested plots when fire frequency increased from zero to seven fires, but was not affected by fire frequency on unharvested plots. The reduction in total AGC associated with increasing fire frequency on harvested plots was driven by declines in large coarse woody debris (≥10cm diameter) and large trees (≥20cm diameter). Small tree (<20cm DBH) AGC increased with fire frequency on harvested plots, but decreased on unharvested plots. Carbon in dead standing trees decreased with increasing fire frequency on unharvested plots, but was unaffected on harvested plots. Small coarse woody debris (<10cm diameter) was largely unaffected by fire frequency and harvesting. Total AGC on harvested plots was between 67% and 82% of that on unharvested plots, depending on burning treatment. Our results suggest that AGC in historically harvested forests may be susceptible to declines in response to increases in prescribed burning frequency. Consideration of historic harvesting will be important in understanding the effect of prescribed burning programs on forest carbon budgets.

Partitioning risks of tree mortality by modes of death in managed and unmanaged northern hardwoods and mixedwoods

We used a permanent sample plot network established to monitor the effects of forest management practiced in mature northern hardwood and mixedwood stands in Québec, Canada to address two important questions related to tree mortality: (1) How does partial cutting affect tree mortality? (2) Which variables best explain tree mortality by different modes of death (standing death, uprooting or stem breakage)? Decennial tree deaths were lower after partial cutting than in unharvested plots, but the annual proportion of tree death was similar (1.25%·year-1). At the tree level, a risk-product classification demonstrated the strongest evidence on influencing total mortality, followed by species, the presence of a logging injury, and tree size. Annual temperature was the only climatic variable explaining variations in total risk of tree mortality, and always among the first three variables explaining differences among the three modes of death. The risk of standing death also increased with increasing annual precipitation, while the risk of stem breakage and, to a lesser extent, of being uprooted, decreased with increasing precipitation. Additionally, we found strong evidence to support the effect of the potassium/magnesium ratio of the humus layer on the risk of being uprooted. This information is critical to better understand tree mortality processes.

Natural Regeneration in a Multi-Layered Pinus sylvestris-Picea abies Forest after Target Diameter Harvest and Soil Scarification

Forest management in Sweden can be characterized by even-aged silviculture heavily relying on three established harvest regimes: clearcutting, the seed-tree method, and the shelterwood system. Less intense, small-scale retention harvest systems such as single tree and group selection harvest are rarely used. In addition, natural regeneration dynamics without enrichment planting have barely been studied. Consequently, this study examined natural regeneration establishment in a multi-layered Pinus sylvestris-Picea abies forest stand in southwest Sweden after target diameter harvesting and soil scarification. The creation of forest canopy gaps had a positive effect on total seedling density five years after harvest, mainly due to a significantly higher number of Betula pendula individuals. Seedling density of more desirable tree species suitable for continuous cover forestry such as Fagus sylvatica, Quercus petraea and Picea abies also increased substantially in gaps when compared to pre-harvest conditions or the unharvested plots. In contrast, soil scarification did not increase the number of seedlings of desired tree species due to a significant decrease in Picea abies abundance. Soil moisture and gap size significantly improved Betula pendula seedling establishment while a larger number of Quercus petraea seedlings were observed in Vaccinium myrtillus patches. We conclude that canopy gaps are beneficial under the encountered stand conditions to initiate forest regeneration, and that soil scarification without the timely occurrence of a mast year of desired tree species is not effective in the type of forest studied.

Plant responses to a phytomanaged urban technosol contaminated by trace elements and polycyclic aromatic hydrocarbons.

Medicago sativa was cultivated at a former harbor facility near Bordeaux (France) to phytomanage a soil contaminated by trace elements (TE) and polycyclic aromatic hydrocarbons (PAH). In parallel, a biotest with Phaseolus vulgaris was carried out on potted soils from 18 sub-sites to assess their phytotoxicity. Total soil TE and PAH concentrations, TE concentrations in the soil pore water, the foliar ionome of M. sativa (at the end of the first growth season) and of Populus nigra growing in situ, the root and shoot biomass and the foliar ionome of P. vulgaris were determined. Despite high total soil TE, soluble TE concentrations were generally low, mainly due to alkaline soil pH (7.8-8.6). Shoot dry weight (DW) yield and foliar ionome of P. vulgaris did not reflect the soil contamination, but its root DW yield decreased at highest soil TE and/or PAH concentrations. Foliar ionomes of M. sativa and P. nigra growing in situ were generally similar to the ones at uncontaminated sites. M. sativa contributed to bioavailable TE stripping by shoot removal (in g ha(-1) harvest(-1)): As 0.9, Cd 0.3, Cr 0.4, Cu 16.1, Ni 2.6, Pb 4, and Zn 134. After 1 year, 72 plant species were identified in the plant community across three subsets: (I) plant community developed on bare soil sowed with M. sativa; (II) plant community developed in unharvested plots dominated by grasses; and (III) plant community developed on unsowed bare soil. The shoot DW yield (in mg ha(-1) harvest(-1)) varied from 1.1 (subset I) to 6.9 (subset II). For subset III, the specific richness was the lowest in plots with the highest phytotoxicity for P. vulgaris.

Windthrow and growth response following a spruce budworm inspired, variable retention harvest in New Brunswick, Canada

Forest management regimes increasingly focus on the emulation of natural disturbance events, e.g., fire or insect outbreaks, to help increase ecosystem sustainability. We determined the residual stand response to a variable retention harvest inspired by spruce budworm (Choristoneura fumiferana (Clemens)) outbreaks in New Brunswick, Canada. Our objectives were to analyze the differences between surviving residual trees and those that succumbed to windthrow and to quantify growth release. The treatment was based on harvesting the estimated spruce budworm outbreak mortality, i.e., 90% of mature balsam fir (Abies balsamea (L.) Mill., 60% of mature spruce (Picea spp.), and no hardwoods. Windthrow increased with the proportion of trees harvested and averaged 52% over 7–9 years in these stands with high balsam fir – spruce content. One-third of 42 harvested plots sustained &gt;30% windthrow, whereas 73% of 11 similar unharvested plots had &lt;10% windthrow. Balsam fir had higher windthrow than spruce at 53% and 41%, respectively. Windthrown balsam fir trees had significantly larger diameters at breast height (DBH, 1.3 m), larger heights, and smaller crown ratios than surviving residual trees. Substantial growth release occurred, with DBH increment of residual trees 48%–64% greater than trees in unharvested plots. Balsam fir and intolerant hardwoods exhibited the largest growth response. We suggest that future spruce budworm inspired harvests in stands with high balsam fir – spruce content use two or three entries about 5 years apart to reduce windthrow.

A harvest method informed by traditional knowledge maximises yield and regeneration post harvest for karengo (Bangiaceae)

Within New Zealand, a group of bladed intertidal algae in the Bangiaceae family known as karengo is harvested entirely from wild stocks and is culturally important for Māori (New Zealand’s indigenous people) both as a food and historically for trade. To sustainably maintain this wild resource, it is important to optimise harvest strategies. Knowledge gained from intergenerational harvest of karengo by Māori communities could provide a sustainable harvest technique. Harvesting trials between July 2013 and August 2013 assessed the effect of a traditional harvest method informed by mātauranga Māori (traditional knowledge), pulling by hand, on the regeneration of karengo. Traditional pulling was compared with cutting and scraping harvest methods. A sustainable harvest technique was determined by assessing yield and post harvest regeneration within the winter growth period from each harvest method. Hand pulling resulted in the greatest biomass regeneration post harvest, providing a 46 % greater yield than scraping and no discernable difference in biomass 6 weeks post harvest compared to unharvested plots. A later harvest (August) resulted in an 83 % greater yield than an early harvest (July). Therefore, to obtain an optimal yield whilst maintaining a sustainable harvest, hand pulling late in the season is recommended. These findings support and strengthen a harvest technique based on mātauranga Māori and provide information to empower kaitiaki (Māori guardians) to actively manage and preserve highly valued wild karengo stocks.

Thinning method and intensity influence long-term mortality trends in a red pine forest

Tree mortality shapes forest development, but rising mortality can represent lost production or an adverse response to changing environmental conditions. Thinning represents a strategy for reducing mortality rates, but different thinning techniques and intensities could have varying impacts depending on how they alter stand structure. We analyzed trends in stand structure, relative density, stand-scale mortality, climate, and correlations between mortality and climate over 46 years of thinning treatments in a red pine forest in Northern Minnesota, USA to examine how thinning techniques that remove trees of different crown classes interact with growing stock manipulation to impact patterns of tree mortality. Relative density in unharvested plots increased during the first 25 years of the study to around 80%, then began to plateau, but was lower (12–62%) in thinned stands. Mortality in unharvested plots claimed 2.5 times more stems yr −1 and 8.6 times as large a proportion of annual biomass increment during the last 21 years of the study compared to the first 25 years, but showed few temporal trends in thinned stands. Mortality in thinning treatments was generally lower than in controls, particularly during the last 21 years of the study when mortality averaged about 0.1% of stems yr −1 and 4% of biomass increment across thinning treatments, but 0.8% of stems yr −1 and 49% of biomass increment in unharvested plots. Treatments that combined thinning from above with low growing stock levels represented an exception, where mortality exceeded biomass production after initial thinning. Mortality averaged less than 0.1% of stems yr −1 and less than 1% of annual biomass production in stands thinned from below. These trends suggest thinning from below minimizes mortality across a wide range of growing stock levels while thinning from above to low growing stock levels can result in dramatic short-term increases in mortality. Moderate to high growing stock levels (21–34 m 2 ha −1) may offer greater flexibility for limiting mortality across a range of thinning methods. Mean and maximum annual and growing season temperatures rose by 0.6–1.8 °C during the study, and temperature variables were positively correlated with mortality in unharvested plots. Mortality increases in unharvested plots, however, were consistent with self-thinning principles and probably not driven by rising temperatures. These results suggest interactions between thinning method and intensity influence mortality reductions associated with thinning, and demonstrate the need for broader consideration of developmental processes as potential explanations for increased tree mortality rates in recent decades.

Impacts of land use, anthropogenic disturbance, and harvesting on an African medicinal liana

African medicinal plant species are increasingly threatened by overexploitation and habitat loss, but little is known about the conservation status and ecology of many medicinal species. Mondia whitei (Apocynaceae, formerly Asclepiadaceae), a medicinal liana found in Sub-Saharan Africa, has been subject to intensive harvesting and habitat loss. We surveyed M. whitei in Kakamega Forest, the largest of three remnant Kenyan forests known to contain the species. In 174 100 m 2 plots, we quantified the status of M. whitei and investigated its relationships with land use, disturbance and harvesting. With average adult densities of 101 plants/ha, M. whitei is not locally rare in Kakamega. However, the absence of flowers and fruits, together with a spatial disconnect between adults and juveniles, suggests that sexual regeneration is patchy or infrequent. Comparing among habitat types, we found that plants were most abundant in regenerating indigenous forest managed by the Forest Department, which permits some extractive uses. Conversely, plants were largest in indigenous forest managed by the Kenya Wildlife Service, which prohibits extractive uses. Most anthropogenic disturbances were not associated with M. whitei, but plant occurrence and density were higher along paths used by livestock than along other types of paths. Larger individuals appeared to be preferentially harvested, but adult plants were more likely to occur in harvested plots than un-harvested plots. This work emphasizes that restrictions on disturbance and extractive use do not automatically promote medicinal plant conservation. Moreover, harvesting may have important genetic and demographic consequences that are overlooked by studies focused on numerical losses.

Aspen regeneration, forage production, and soil compaction on harvested and grazed boreal aspen stands

The objective of our study was to determine the effects of timber harvesting and cattle grazing on aspen regeneration, forage production, and soil compaction on aspen cutblocks in the Peace River region of British Columbia. This project was carried out on a long-term study site established 5 km south of Dawson Creek, B.C. Samples were collected and vegetation was assessed during the summer of 2002. Summer and winter harvesting significantly increased aspen stem density relative to unharvested plots, whereas 4 years of cattle grazing had no significant impact on stem density. Inter-tree spacing remained above the postulated minimum of 60-80 cm, indicating that livestock can access the stand. Timber harvesting increased forage production by 69%, while grazing had no effect on forage production. Soil penetration resistance was similar for three harvesting treatments down to a 21 cm depth, while between 21 and 60 cm penetration resistance was consistently the highest on summer-harvested plots, followed by winter-harvested and unharvested plots. Grazing had no impact on soil penetration resistance. The results of this study support the view that cattle grazing and aspen harvesting are complementary land uses for aspen cutblocks on similar sites in the Peace River region; however, proper planning is required to avoid potential cattle distribution problems.

Effects of clam harvesting on sexual reproduction of the seagrass Zostera noltii

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 298:115-122 (2005) - doi:10.3354/meps298115 Effects of clam harvesting on sexual reproduction of the seagrass Zostera noltii Ana Alexandre*, Rui Santos, Ester Serrão Marine Plant Ecology Research Group, CCMAR - Centro de Ciências do Mar, CIMAR - Laboratório Associado, Universidade do Algarve, Gambelas, 8005-139 Faro, Portugal *Email: aalexandre@ualg.pt ABSTRACT: The sexual reproduction of Zostera noltii in the Ria Formosa lagoon (southern Portugal) was assessed by quantifying the variation in both flowering effort and evolution of maturation stages during the fertile season. The effects of clam harvesting on the sexual reproduction of Z. noltii were investigated using both descriptive and experimental approaches. Meadows disturbed by clam harvesting were compared with undisturbed meadows in 2 sectors of the lagoon. In both sectors, disturbed meadows showed significantly lower vegetative shoot density and significantly higher reproductive effort. The reproductive effort in the western disturbed meadows was 2-fold higher than in undisturbed meadows, whereas in eastern disturbed meadows it was 4-fold higher. In disturbed meadows, early maturation stages were found until the end of the flowering season and higher seed production was observed. Both the negative effect of clam harvesting on Z. noltii density and the positive effect on its reproductive effort were confirmed by manipulative field experiments. Plots that were experimentally harvested during the fertile season showed significantly lower vegetative shoot density and higher reproductive effort than unharvested plots. Results suggest that Z. noltii responds to clam harvesting disturbance by both increasing its reproductive effort and extending its fertile season. KEY WORDS: Zostera noltii · Clam harvesting · Sexual reproduction · Maturation scale · Disturbance · Flowering Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 298. Online publication date: August 15, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Habitat manipulation in lucerne Medicago sativa: arthropod population dynamics in harvested and ‘refuge’ crop strips

Summary In order to realize the full potential of natural enemies in integrated pest management, it is necessary to understand their population dynamics, particularly in relation to the role of refuges. Harvested and unharvested plots were established in a commercial hay lucerne Medicago sativa crop and the potential for the unharvested vegetation to constitute a refuge for natural enemies of Helicoverpa spp., one of the key pests, was evaluated. The temporal and spatial dynamics of arthropod populations were evaluated using sequential samples from directional traps (pitfall and Malaise) and vacuum sampling in both crop treatments. The spatial dynamics of predation were measured using ‘sentinel’ cards baited with Helicoverpa spp. eggs. There was no significant directional movement of arthropods captured in pitfall traps, except for a 3‐day period immediately after harvest when there was a net movement of the natural enemies Dicranolaius bellulus, Carabidae adults, spiders and the phytophagous mite Halotydeus destructor from harvested to unharvested plots. There was net movement of adult Netelia producta, D. bellulus, Coccinella transversalis and Syrphidae as well as the pest Helicoverpa spp. from harvested to unharvested plots for 24 h following a harvest. Densities of D. bellulus and C. transversalis within unharvested plots decreased with increasing distance from the borders with harvested plots. Predation rates of Helicoverpa eggs placed in unharvested plots were broadly consistent with predator densities and decreased with distance from the harvested plots. Predation rates of Helicoverpa eggs placed in harvested plots declined with increasing distance from unharvested plots, suggesting that natural enemies from the latter dispersed into regrowing lucerne. Strips narrower than the plot width used (30 m) may be adequate to accommodate natural enemies displaced by harvesting. Unharvested refuge strips should ideally be spaced less than 30 m apart so that the natural enemies can contribute to biological control of pests over the entire width of harvested strips.

Short-term changes in soil C, N, and biota following harvesting and regeneration of loblolly pine ( Pinus taeda L.)

In affiliation with the USDA-FS long-term soil productivity program, a series of studies have been established in the US gulf coast region to monitor the effects of intensive silviculture on site productivity. This report presents early results of a study of the interactive effects of harvest intensity and cultural treatments on soil C, N, and biological processes following the regeneration of two stands of loblolly pine ( Pinus taeda L.), a 19-year-old stand in St. Helena Pa., LA and a 27-year-old stand in Tyler Co., TX. Two harvesting intensities (MWT, mechanical whole-tree and HFBO, hand felled bole-only removed) were combined in a factorial assignment with bedding and herbaceous weed control (at St. Helena) or bedding and fertilization (at Tyler). Total C and N in 0–15 cm of soil were determined before, 9 and 21 months after harvesting. Total C and N in 0–60 cm were measured 2 years after harvesting at St. Helena and 3 years after harvesting at Tyler. At Tyler, N mineralization, soil respiration, and microbial populations were monitored before and for 2 years after harvesting. In the 19-year-old stand, MWT removed 67% of the above-ground biomass and 38% of the above-ground N compared to 46% and 10% for HFBO. In the 27-year-old stand, MWT removed 62% of the biomass and 35% of the N, while HFBO removed 48% and 13%. Harvesting method had no effect on total C or total N in surface soil but bedding resulted in higher levels of both 1 years after harvesting. The effect of bedding was still detected 3 years after treatment at Tyler but not at St. Helena. Herbaceous weed control at St. Helena had no effect on total N in the surface 60 cm of soil but significantly reduced total C at 30–60 cm 6 months after treatment. Sixteen months after application of 250 kg ha −1 of diammonium phosphate (DAP) at Tyler, the surface 60 cm of mineral soil in fertilized plots averaged 373 kg ha −1 more total N than did soil from unfertilized plots. Total C in the surface 60 cm was not effected by fertilization. Irrespective of harvesting or cultural treatment, total C and total N in the surface 15 cm of soil declined at both sites during the first year after harvesting. The declines were 8.2 Mg ha −1 total C, 361 kg ha −1 total N at St. Helena and 7.6 Mg ha −1 total C, 380 kg ha −1 total N at Tyler. After 2 years, total C and total N had returned to >90% of pre-harvest levels at both locations. Harvesting intensity had no effect on soil temperature, soil respiration, N mineralization, or microbial populations, but bedding significantly increased soil respiration and N mineralization during the first growing season after harvesting. Net N mineralization was not effected by treatments during the second year after harvesting, but was lower in the harvested plots than in the unharvested reference and inversely related to the pre-harvest rate. Fertilization with DAP increased mineral N flux for 2 months following application, but to a lessor extent than did bedding. Nitrification was significantly greater than ammonification in all treatments during the first year after harvesting but was equal to or less than ammonification during the second growing season and in unharvested plots. In these US gulf coast pine stands, harvesting and regeneration resulted in significant but transitory perturbation in soil processes. All of the processes studies returned to or near pre-harvest levels after two growing seasons. Differences in surface biomass removal, between whole-tree and bole-only harvesting, had no measurable effect on the monitored soil processes during the first two growing seasons after harvesting although differences may appear later in the rotation. Harvesting, per se, resulted in an increase in nitrification but no increase in net N mineralization. Bedding incorporated surface organic matter, accelerated microbial activity, and increased net N mineralization but before planted pine seedlings could benefit from the increased N availability. A prolonged release of nutrients from the undisturbed surface residues may be more beneficial to productivity of the pine regeneration than the rapid mineralization which followed bedding.

Short-term responses by ants (Hymenoptera: Formicidae) to selective timber harvesting of an open forest in eastern Australia

Summary In order to determine how timber harvesting might affect the ant community in a Corymbia variegata dominated open forest, the surface-active ant community was quantified by pitfall trapping at two sites and on three occasions over a period of 12 months. At the end of this period, the trees in some plots were experimentally harvested while others remained undisturbed. Pitfall trapping continued for another 12 months at all plots which permitted a comparison between the pre-harvest ant communities and post-harvest ant communities. Using a combination of univariate and multivariate analyses, only small differences could be detected in ant community composition in harvested plots when compared with unharvested plots, indicating that timber harvesting operations such as the ones examined in this study have only a small effect on the structure of the ant community.

Response of ecto- and arbuscular mycorrhizal fungi to clear-cutting and the application of chipped aspen wood in a mixedwood site in Alberta, Canada

Ecto- and arbuscular mycorrhizal (AM) response to clear-cutting and the application of 5 and 10 cm deep layers of chipped aspen wood was determined in a boreal, mixedwood site dominated by aspen poplar ( Populus tremuloides), a species which suckers readily following disturbance. Forest floor disturbance was kept to a minimum during and following clear-cutting. One and two years after clear-cutting and wood chip application, aspen roots in uncut, clear-cut, and clear-cut plus application of a 5 cm or 10 cm layer of wood chips were examined for their ectomycorrhizal (EM) status while roots of the grass, Calamagrostis canadensis, were assessed for their AM status. There was extensive mortality of aspen roots during the first 2 years after cutting although many roots persisted for 1 year and small pockets of regenerating roots were detected after 2 years. Percent mycorrhizal colonization of aspen roots was 90–100% in all treatments over the term of the study indicating that the inoculum potential of the EM fungi was maintained for 2 years post-harvest. Cenococcum geophilum, Cortinarius spp., Russula spp. and Tomentella spp. were abundant on roots from all treatments. Clear-cutting and wood chip application did not seem to reduce the regeneration potential of these fungi over the short-term. In addition to the aforementioned genera, Piloderma byssinum occurred frequently in the unharvested plots, Mycelium radicis atrovirens was common in plots which had received 5 cm of wood chips while Hebeloma was abundant in plots spread with 10 cm of wood chips. With the exception of the 10 cm wood chip treatment, the majority of aspen mycorrhizae were formed by fungi which produce microscopic, resupinate or hypogeous fruitbodies rather than large fleshy fruitbodies. AM colonization of C. canadensis roots was inhibited by the application of 10 cm of wood chips but was unaffected by harvesting and the application of 5 cm of wood chips. Short-term effects of clear-cutting and wood chip treatment on the colonizing abilities of EM and AM fungi appeared to be minimal; long-term impacts require further monitoring.